#mask,
#hint{
    position: fixed;
}
#mask{
    top:0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.7);
    z-index: 200;
    display: none;
    text-align: center;
}
#hint{
    top: 50%;
    left: 50%;
    width: 300px;
    height: 140px;
    line-height: 140px;
    margin-top: -70px;
    margin-left: -150px;
    background: #fff;
    border: 1px solid #c5c5c5;
    border-radius: 4px;
    text-align: center;
    font-size: 24px;
}